Borehole-to-surface electromagnetic (EM) methods are an attractive alternative to surface-based EM<br>methods for a variety of environmental and engineering applications. They have improved sensitivity to the<br>subsurface resistivity distribution because of the closer proximity to the area of interest offered by the borehole<br>for the source or the receiver. For the borehole-to-surface measurements the source is in the borehole and the<br>receivers are on the surface. On the other hand, for the surface-to-borehole methods, the source is on the<br>surface and the receiver is in a borehole. The surface-to-borehole method has an added advantage since<br>measurements are often more accurate due to the lower noise environment for the receiver. For these methods,<br>the source can be a grounded electric dipole or a vertical magnetic dipole source. An added benefit of these<br>techniques is tield measurements are made using a variety of arrays where the system is tailored to the<br>application and where one can take advantage of some new imaging methods. In this short paper we describe<br>the application of the borehole-to-surface method, discuss benefits and shortcomings, and give two field<br>examples where they have been used for underground imaging.


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